Stability of the implant/abutment joint in a single-tooth external-hexagon implant system: clinical and mechanical review

Rigorous efforts have recently been made to reduce the recurrence of implant/abutment joint failure in single‐tooth implant restorations. However, the current knowledge about the stability of implant/abutment joints in an external hexagon implant system is incomplete. We reviewed clinical data regarding single‐tooth implant treatment with Brånemark implants, specifically the CeraOne abutment system (Nobel Biocare AB, Göteborg, Sweden). In vitro studies on joint stability were systematically assessed. Bending overload and the presence of misfit at the implant/abutment joint interface are the critical mechanical conditions that can make the joint unstable. Appropriate joint fitness and proper alignment of the implant should be assessed, and occlusal adjustment by narrowing the restoration width and flattening cuspal inclination should be applied to avoid bending moments caused by the lateral component of occlusal forces. Sufficient clinical reports of longer duration that evaluate and verify longer‐term success of the newly manufactured joint components were unavailable.     

Abrasion of abutment screw coated with TiN

STATEMENT OF PROBLEM

Screw loosening has been a common complication and still reported frequently.

PURPOSE

The purpose of this study was to evaluate abrasion of the implant fixture and TiN coated abutment screw after repeated delivery and removal with universal measuring microscope.

MATERIAL AND METHODS

Implant systems used for this study were Osstem and 3i. Seven pairs of implant fixtures, abutments and abutment screws for each system were selected and all the fixtures were perpendicularly mounted in liquid unsaturated polyesther with dental surveyor. After 20 times of repeated closing and opening test, the evaluation for the change of inner surface of implant and TiN-coated abutment screw, and weight loss were measured. Mann-Whitney test with SPSS statistical software for Window was applied to analyze the measurement of weight loss.

RESULTS

TiN-coated abutment screws of Osstem and 3i showed lesser loss of weight than non-coated those of Osstem and 3i (P < .05, Mann-Whitney test).

CONCLUSION

Conclusively, TiN coating of abutment screw showed better resistance to abrasion than titanium abutment screw. It was concluded that TiN coating of abutment screw would reduce the loss of preload with good abrasion resistance and low coefficient of friction, and help to maintain screw joint stability.     

An abutment screw loosening study of a Diamond Like Carbon-coated CP titanium implant

The aim of this study was to quantify the extent of abutment screw loosening and thus understand the role of frictional and wear factors in abutment screw loosening by using a cyclic loading device to compare Diamond Like Carbon (DLC)-coated and non-coated implants. The properties of DLC films, including hardness, wear resistance, chemical stability, and biocompatibility, are similar to those of real diamond materials. In this study, a 1-mum thick DLC film served to protect and lubricate a layer of commercially-pure titanium affixed to the top of a dental implant (external hexagon-shaped implant). A cyclic loading force was then applied to the top of the prosthetic portion of the implants in order to determine the difference in looseness of the titanium abutment screw between ten DLC-coated implants and ten non-coated implants. The abutment screw loosening tests were performed with 100 N of force at a frequency of 20 Hz. Data indicate that implants with a DLC coating are more resistant to an applied force (P = 0.002) than are those without the coating. We hope these results will be useful for preventing implant abutment screw loosening.     

改变摩擦系数对固位螺丝稳定影响的实验研究

目的探讨摩擦系数的减小对种植体固位螺丝松动的影响.方法用32Ncm将种植体和基台用固位螺丝固定在支持物上,涂布凡士林于固位螺丝表面.保持静止状态和放进超声波震荡器中1h对比,用FG-101数显力矩扳手握住螺丝刀将每个固位螺丝松动,记录测量读数最大值.结果旋松扭矩分别为静止对照组26.7±2.00Ncm,实验组25±1.15Ncm;运动对照组26.1±1.20Ncm,实验组24.8±0.70Ncm.实验组比对照组的旋松扭矩小,两两比较有统计学意义(P＜0.05).结论基台和固位螺丝之间的摩擦系数减小,预负荷增加,但更易松动.     

A technique for repairing a loosening abutment screw for a cement-retained implant prosthesis

Prostheses may be attached to implants or implant abutments using screw retention or cementation. With the increased use of cement-retained, implant-supported restorations for the replacement of missing teeth, clinicians may choose to use a definitive cement to lute the definitive restoration. Loosening of an abutment screw is a challenging complication of cement-retained, implant-supported prosthetic restorations. Often, the abutment screw becomes loose from the implant body, whereas the crown remains cemented to the abutment. In such situations, separating the cemented crown from the underlying abutment or locating the abutment-screw access for removal of the restoration is a difficult task. The purpose of this report is to describe a simple technique for locating the abutment-screw access in the event of its loosening. The advantage of this technique is that it can facilitate easy location of the abutment screw, thus minimizing damage to the existing restoration and allowing it to be reused.     

Retrospective analysis of the influence of abutment structure design on the success of implant unit. A 3-year controlled follow-up study

A comparative study of 96 Spline and Threadloc implants is presented. The authors examined the possibility of the failure of the retaining screws of two different antirotational systems (the Threadloc system with hexagonal polyhedral extension and the Spline system), and the possible incorrect link between the abutment and the transfer. After an observation period of 36 months starting from the day of prosthesis insertion, three single Threadloc fixtures (20%) and five pairs of joint Threadloc fixtures (5.7%) presented problems and a partial prosthetic screw loosening. For the Spline series fixtures, no screw loosening was encountered. Regarding the safety of the link between abutment and implant, the best results were obtained from the Spline system, which did not hinder the dentist in positioning the link with the abutment. This is the result of the different geometries of the two antirotational mechanisms which are present on the two fixtures. It is believed that the precise contact between the abutment and the fixture avoids the triggering of a phlogistic process, which can develop into periimplantitis. Therefore, when hex systems are used, an x-ray, which verifies this correct situation, is always recommended during the follow-up.     

The Use of a Dental Surgical Microscope to Aid Retrieval of a Fractured Implant Abutment Screw: A Clinical Report

This clinical report outlines a method to retrieve a fractured implant abutment screw through the use of high‐power magnification and ultrasonic instrumentation. Furthermore, the use of manufacturer's specific components is highlighted to minimize occurrences of such clinical complications from arising.     

Abutment screw loosening and bending resistance of external hexagon implant system after lateral cyclic loading

Background: Rigorous efforts to reduce the recurrence of abutment screw loosening in single‐tooth implant restorations have recently been made. However, the behavior of the implant/abutment joint components with respect to critical bending force is still unclear. Purpose: This study investigated the effect of different cyclic loading periods on abutment screw loosening and bending resistance of a single‐tooth external hexagon implant system. Material and Methods: Fifteen Brånemark implant assemblies were divided equally into groups A, B, and C. Each assembly consisted of a Brånemark System® Mk IV 4 × 10 mm implant (Nobel Biocare AB, Gothenburg, Sweden) mounted in a brass block, a CeraOne® 3 mm abutment (Nobel Biocare AB), and an experimental cement‐retained superstructure. For groups A and B a cyclic load of 50 N was applied centrally and perpendicular to the long axis of the implant. Targets of 1.0 × 10⁶ cycles (40 months of simulated function) and 0.5 × 10⁶ cycles (20 months of simulated function) were defined for groups A and B, respectively. Group C (control) was left unloaded for the same loading time period as was group B. Reverse torque was recorded before and after loading, and the difference was calculated. After cyclic loading, specimens were mounted in a testing machine, and the yielding and bending strengths were measured. The data were analyzed with one‐way analysis of variance and were compared by means of the Tukey test (p < .05). Results: There were statistically significant differences (p < .001) in the reverse torque difference values of group A ([‐5.6 to ‐3.41 ± 0.86 Ncm) as compared to those of group B ([‐2.4 to ‐1.61 ± 0.32 Ncm) and group C ((‐0.7 to 0.01 ± 0.26 Ncm). Likewise, group B showed a significant difference compared to group C (p= .002). On the other hand there was no statistically significant difference in the mean values among the test groups in regard to the yielding and bending strengths (p >.050). Conclusion: Within the limitations of this study, long‐term fatigue significantly affected the reverse torque values under centric lateral load (p <.001) whereas it had no significant effect on the resistance of the implant/abutment joint to static bending.     

Effect of implant abutment connection designs,and implant diameters on screw loosening before and after cyclic loading: In-vitro study

AimsThe purpose of this in-vitro study was to evaluate the screw loosening of two different forms of implant abutment connection designs, and two implant diameters by measuring removal torque value (RTV) before and after cyclic loading.Materials and methodsTwenty implant fixtures were divided equally into 2 groups (N = 10): group I fixture with conical hybrid connection (CH), and group II fixture with internal hex connection (IH). Each group was divided equally into two subgroups according to implant diameters: subgroup A (3.3 mm), and subgroup B (4.2 mm). Each fixture was vertically placed in the center of an acrylic resin block. The samples were fixed to the jig, and an implant abutment connected it with a 20 Ncm tightening torque. The samples were subjected to eccentric cyclic loading (at a distance of 5 mm) away from center of abutment at 100,000 cycles. A digital torque gauge was used to evaluate screw loosening by measuring RTVs in (Ncm) before and after cyclic loading. The removal torque loss ratio before and after cyclic loading and the removal torque loss ratio between before and after cyclic loading were calculated and analyzed using the SPSS statistical analysis.ResultsFor GI the initial removal torque loss ratio measurement was (14.45 ± 3.18) and decreased significantly after loading, it was (11.47 ± 3.64). For GII the initial removal torque loss ratio measurement was (20.47 ± 4.99) and increased significantly after loading, being (35.35 ± 4.26). There is no significant effect upon screw loosening for two implant diameters.ConclusionWithin the limitations of this study, the results suggested that conical hybrid connections showed a better screw stability than an internal hex connection. Therefore, the use of conical implants can be promoted as they have better screw stability compared to other systems.     

Influence of implant abutment angulations on the fracture resistance of overlaying CAM-milled zirconia single crowns

Background: An in vitro study was performed to assess the effect of three implant abutment angulations and three core thicknesses on the fracture resistance of overlaying computer‐aided manufacturing (CAM) milled zirconia (Cercon^® system) single crowns. Methods: Three groups, coded A to C, with different implant abutment angulations (group A/0°, group B/15° and group C/30° angulation) were used to construct 15 crowns for each angulation. Forty‐five overlay restorations were milled using the Cercon^® system with zirconium core thicknesses of 0.4, 0.6 and 0.8 mm using five crowns for each angulation. The final restorations were prepared and stored in distilled water at mouth temperature (37 °C) for 24 hours prior to testing. The restorations were cemented using Temp Bond^®. The load required to break each crown and the mode of failure were recorded. All the results obtained were statistically analysed by the ANOVA test (level of significance p < 0.05). Tested crowns were examined using a stereomicroscope at 40X and selected crowns (five randomly selected from each group were further examined by scanning electron microscopy) to reveal the zirconia–ceramic interface and to determine the fracture origin. Results: Implant abutment angulations significantly (p < 0.05) reduced the fracture resistance of overlaying CAM‐milled zirconia single crowns. The fracture loads of Cercon^® crowns cemented onto abutment preparations with a 30° angulation were the lowest of the groups tested. The core thickness (0.4 to 0.8 mm) did not significantly (p > 0.05) affect the fracture resistance of the CAM‐milled zirconia single crowns. SEM showed that the origin of the fracture appeared to be located at the occlusal surfaces of the crowns and the crack propagation tended to radiate from the occlusal surface towards the gingival margin. Conclusions: The implant angulation of 30° significantly (p < 0.05) reduced the fracture resistance of overlaying CAM‐milled zirconia single crowns. Reducing the core thickness from 0.8 mm to 0.4 mm did not affect (p > 0.05) the fracture resistance of overlaying CAM‐milled zirconia single crowns.     

反复松紧过程对种植体与基桩结合稳定性的影响

目的探讨在调整TiAdap基桩时,反复松紧过程对种植体和基桩的结合稳定性是否有影响。方法15个Branemark种植体(5RP,5NP,5WP)分别与5个TiAdapRP,5个TiAdaptNP、5个TiAdaptWP组成3组,3组分别用32N.cm、20N.cm、45N.cm扭力将种植体和基桩拧紧,然后再用扭力控制仪将两者松开,记录扭力的数据,重复5次。结果方差分析显示5次拧紧-松开过程记录的扭力第1组无显著性差异(P=0.5319);而第2、3组存在显著性差异(P=0.0084,0.0049),差别主要存在于第1次拧紧-松开过程和后4次松紧之间,后4次松紧过程之间无显著性差异。结论表明反复松紧过程对种植体和基桩结合稳定性的影响主要在第1次松紧过程。     

Effects of modified abutment characteristics on peri‐implant soft tissue health: A systematic review and meta‐analysis

Objectives

The purpose of this systematic review was to evaluate the impact of the abutment characteristics on peri‐implant tissue health and to identify the most suitable material and surface characteristics.

Methods

A protocol was developed aimed to answer the following focused question: “Which is the effect of the modification of the abutment design in regard to the maintenance of the peri‐implant soft tissue health?” Further subanalysis aimed to investigate the impact of the abutment material, macroscopic design, surface topography and surface manipulation. Randomised controlled trials (RCTs) with a follow‐up of at least 6 months after implant loading were considered as inclusion criteria. Meta‐analyses were performed whenever possible.

Results

Nineteen final publications from thirteen investigations were included. The results from the meta‐analysis indicated that zirconia abutments (Zi) experienced less increase in BOP values over time [n = 3; WMD = ?26.96; 95% CI (?45.00; ?8.92); p = .003] and less plaque accumulation [n = 1; MD = ?20.00; 95% CI (?41.47; 1.47); p = .068] when compared with titanium abutments (Ti). Bone loss was influenced by the method of abutment decontamination [n = 1; MD = ?0.44; 95% CI (?0.65; ?0.23); p < .001]. The rest of the studied outcomes did not show statistically significant differences.

Conclusions

The macroscopic design, the surface topography and the manipulation of the implant abutment did not have a significant influence on peri‐implant inflammation. In contrast, the abutment material demonstrated increased BOP values over time for Ti when compared to Zi abutments.

     

Immediate and delayed loading of fixed dental prostheses supported by single or two splinted implants: A histomorphometric study in dogs

To evaluate presumptive differences in osseointegration at implants supporting crowns that are physiologically loaded either immediately or 3 months after installation. All premolars and first molars were extracted bilaterally in six dogs. After 3 months of healing, three implants were installed on the premolar region and two in the molar region in one side of the mandible. Likewise, after another 3 months, five implants were installed in the contralateral side, and impressions were taken bilaterally. Within 48 hours, two single crowns were screwed bilaterally onto two implants in the premolar region, and two splinted crowns reproducing the shape of the first molar were screwed bilaterally onto the implants in the molar region. The mesial implants were used as no‐loaded controls. Sacrifices were performed after 3 months, and histological analyses were performed. At the premolar sites, mineralised bone‐to‐implant contact (MBIC%) was 78.0 ± 4.0% and 70.9 ± 7.9% at the delayed and immediately loaded sites, respectively. This difference was statistically significant. At the control implants, MBIC% was 61.4 ± 14.7% and 63.1 ± 13.1% at the delayed and the immediately loaded sites, respectively. At the molar sites, MBIC% was 79.2 ± 10.9% and 61.1 ± 10.3% at the delayed and immediately loaded sites, respectively. Applying a delayed loading to fixed dental prostheses supported by single or two splinted implants yielded higher proportions of bone‐to‐implant contact (osseointegration) compared to immediately loaded implants. Moreover, both types of loading protocols yielded a higher rate of osseointegration compared to unloaded implant sites after 3 months following implant installation.